Symptoms and causes


Signs and symptoms that might be associated with blastocystis include:

  • Diarrhea
  • Nausea
  • Abdominal cramps
  • Bloating
  • Excessive gas (flatulence)
  • Hives
  • Loss of appetite
  • Fatigue

When to see a doctor

See your doctor if you have signs and symptoms, such as diarrhea or cramps, that last longer than three days.


Once thought to be a harmless yeast, blastocystis is a parasite — a microscopic single-celled organism (protozoan). Many protozoans normally inhabit your gastrointestinal tract and are harmless or even helpful; others cause disease.

Whether blastocystis is the type of protozoa that causes disease is controversial. While many people who carry blastocystis have no signs or symptoms, the organism is also found in people who have diarrhea and other digestive problems. Blastocystis often appears with other organisms, so it's not clear whether it causes disease on its own or is an innocent bystander.

It's also possible that some people may be carriers of blastocystis. These carriers don't have any signs or symptoms of infection. And, the incidence of symptoms doesn't go up with an increase in the number of parasites.

Although no one knows for sure how blastocystis gets into the digestive system, experts suspect that blastocystis may get into the intestinal tract through oral-fecal contact. This can occur when a person doesn't wash his or her hands thoroughly after using the toilet before preparing food. The prevalence of blastocystis increases in places with inadequate sanitation and poor personal hygiene.

Risk factors

Blastocystis is common, and anyone can have the organism in his or her stools. You may be at higher risk if you travel or live where sanitation is inadequate or where the water may not be safe.


If you have diarrhea associated with blastocystis, it's likely to be self-limiting. However, anytime you have diarrhea, you lose vital fluids, salts and minerals, which can lead to dehydration. Children are especially vulnerable to dehydration.

Aug. 08, 2017
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